Sargassum, a type of brown floating algae, has shifted its range in recent decades — thinning out in the North Atlantic’s Sargasso Sea while proliferating in the tropical Atlantic. That trend, underway since 2011, continued in 2026: the algae reached its annual peak in June across a stretch of ocean known as the Great Atlantic Sargassum Belt, with both the Caribbean Sea and the Gulf of America hitting all-time highs.
That said, sargassum levels can change week to week, so it’s worth checking Belize forecasts, NOAA/AOML reports, and local operator updates before you travel — especially during peak season (June–October). Live map links and local forecasts are below so you can track conditions as your trip approaches.
Sargassum seaweed is a free-floating brown seaweed that originates in the Sargasso Sea and the equatorial Atlantic. Since 2011, a weather pattern shift has caused enormous quantities to wash into the Caribbean, including Belize’s coastline, each year. That geography, where Belize sits in the Caribbean, is exactly why east-facing beaches catch the drift each summer while inland Belize never does.
Historically, the majority of Sargassum aggregated in the Sargasso Sea in the western North Atlantic, with some small amounts found within the Gulf of America and Caribbean Sea. In 2011, the geographic range expanded, and massive amounts of Sargassum moved west into the Caribbean Sea, Gulf of America, and tropical Atlantic, washing ashore in Florida, Puerto Rico, the US Virgin Islands, and most islands and coastal areas in the Caribbean Sea and Western Africa.
The main season runs roughly March through October, peaking June to August. Arrivals vary week to week with wind and currents, which is exactly why a live map beats a static seasonal chart. For month-by-month planning, see our full Belize sargassum guide.
Exposure varies dramatically by location. The barrier reef, prevailing winds, and beach orientation determine how much sargassum any given stretch receives, from Ambergris Caye and San Pedro in Belize to Hopkins and Placencia. Here is the honest regional picture.
Since 2011, large accumulations of Sargassum have occurred every year in the Caribbean Sea, Gulf of America, and tropical Atlantic, but the amount can vary from year to year.
The presence of Sargassum occurs over large areas from the tropical Atlantic in the east, to the Gulf of America in the west, approximately 5,000 kilometers from the eastern tropical Atlantic to the west off the Mexican coast in the Caribbean Sea. Sargassum does not extend as a blanket (or blob) covering the full surface of the ocean in these regions. Instead, Sargassum floats in patches that range in size from a few centimeters to hundreds of meters. Some of these patches reach the coastal areas, including beaches, ports, and even intake systems for drinking water. The area that these patches cover has been significantly larger in recent years than prior to 2011.
Satellite sensors can estimate indicators related to Sargassum coverage, which enable us to quantify the area affected and estimate the volume of Sargassum in a specific region.
Sargassum, in normal amounts, provides habitat, food, protection, and breeding grounds for hundreds of diverse marine species, including commercially important species, such as tuna and swordfish, that feed on the smaller marine life present in Sargassum mats. If Sargassum reaches the coast in small/normal quantities, it may help to avoid beach erosion.
Out at sea, Sargassum is an important habitat for fish, sea turtles, and other marine organisms, but as it accumulates close to the coastlines it can smother valuable corals, seagrass beds, and beaches. As it washes ashore the seaweed begins to decay, attracting flies and other insects. Additionally, during its breakdown, Sargassum produces hydrogen sulfide gas, which smells of rotten eggs, repelling beachgoers and affecting the tourism industry that depends on pristine ocean conditions. Sargassum can also impact navigation, block water intake in desalination plants, and impact benthic ecosystems after/if they sink to the bottom of the ocean.
Studies of the impact of Sargassum on human health started very recently and this is a topic that needs more time to be fully understood. However, when decomposed, Sargassum releases hydrogen sulfide (a gas) that may cause respiratory health problems. Sargassum is also known to often contain heavy metals that can be toxic to humans and animals. In addition, recent studies have found that Sargassum mats can harbor pathogenic Vibrio bacteria, which can lead to skin infections or gastrointestinal illness from direct contact or consumption of contaminated seafood, particularly in vulnerable individuals.
A Sargassum day is not a wasted day. Belize has more ways to spend a morning than beach access, and most of them are better than the beach anyway. The best alternative to a beach day: swap it for an inland one, headlined by the ATM Cave, a full-day Maya cave tour with zero seaweed exposure of any kind.
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